1. Field of the Invention
This invention relates to a process and device for slaving the frequency and phase of an oscillator, specifically a voltage-controlled crystal oscillator. More particularly, the process and device of the invention include slaving the operation of a crystal oscillator against an external signal provided in the form of periodic bursts.
2. Discussion of the Related Art
Voltage-controlled crystal oscillators have been known for a long time. Notably, French patent number FR-1.473.273 teaches a crystal oscillator whose operating frequency is controlled according to an electric control signal, such as a voltage level, whose variations produce almost linear variations in the oscillator's operating frequency. Crystal oscillator circuits of this kind have also been described more recently in French and European patent applications numbers FR-2.569.505 and BP-466.388 respectively.
Devices for slaving the frequency and phase of a crystal-controlled oscillator against a reference signal have also been known for a long time. For example, French patent application number FR-2.620.878, filed in the name of THOMSON-CSF, proposes a crystal oscillator whose operating frequency is thermally controlled. A mechanism is provided in particular to heat the crystal which, according to a measured frequency and phase difference, modifies the temperature of the crystal and therefore its operating frequency. Other temperature-controlled crystal oscillators are also described in European patent application number EP-401.919.
Special control loops for locking short-term stable oscillation against long-term stable oscillation are also known and taught in French patent applications numbers FR-2.626.686 and FR-2.614.116. Such control loops are used, for example, in the telecommunications field to match working frequencies with atomic standard frequencies.
European patent application number EP-0.230.900 describes a device for rhythms recovery. In one embodiment, the signal is sampled and digitized. The sign of the signal, being related to the estimated error, is then determined and directed to a sequential logic. This logic produces, through an analogic logical interface, a command signal for the sampler. In this device, solely the sign of the estimated error is considered.
The present invention proposes a process and device for slaving the frequency and phase of an oscillator, particularly a voltage-controlled crystal oscillator, which is novel and includes the advantage that it allows the control loop of the crystal oscillator to be processed mainly in digital fashion.
An object of this invention is to provide a process for slaving the frequency and phase of a crystal oscillator against a reference signal, the crystal oscillator being controlled in frequency and phase by a physical control magnitude.